“Living” polymerizations provide materials with well-defined chain lengths and narrow molecular weight distributions (polydispersity indices or PDIs). They also allow the preparation of block polymers. Among the general classes of living polymerizations, ring opening metathesis polymerization (ROMP) has been broadly applied for the synthesis of materials with interesting physical properties1 and biological activities.2,3 
Although ROMP polymers have been prepared from many strained cycloalkenes and their derivatives,4 norbornenes and oxanorbornenes are typically used for the preparation of peptide- and carbohydrate-bearing multivalent ROMP polymers.3,5 These monomers, substituted on the 5-position or on the 5- and 6-positions of the norbornene ring, are the most synthetically accessible monomers that metathesize efficiently. However, in these systems, stereocontrol of the polymerization reaction is not always possible. For example, ruthenium-catalyzed polymerization of 5-substituted norbornene and oxanorbornene monomers provides stereochemically heterogeneous materials.6 Each monomeric unit contributes three stereochemical variables that are not controlled in the chain extension step.7 Therefore it is difficult to correlate the physical or biological properties of these polymers with specific structural features.
The literature offers several examples of the ROMP and ROM (ring opening metathesis) of substituted cyclobutenes9-12 including three examples in which the substrate is a 1-substituted cyclobutene.12 Indeed, with the (CO)5WC(C6H5)2 catalyst, Katz and coworkers produced translationally invariant (all head-to-tail, E-olefinic) polymer from 1-methylcyclobutene and from 1-trimethylsilylcyclobutene.12d Nonetheless, it was unexpected that the more functional group-tolerant ruthenium catalysts would give analogous results with related monomers that bear functional groups, such as amide functional groups.
Ring opening metathesis polymerization is especially unpredictable when conducted with monomers that are cyclic unsaturated amides, especially those in which a conjugated double bond is in the ring. Neither the regiochemistry of the ring opening nor the geometry of the resulting double bond in the polymer could have been predicted.